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Date of Award

3-18-2016

Document Type

Thesis and Dissertation-ISU Access Only

Degree Name

Master of Science (MS)

Department

Department of Geography-Geology: Hydrogeology

First Advisor

Eric W. Peterson

Abstract

Groundwater modeling plays an important role in quantifying solute transport in watersheds. Many watersheds contain developed or urbanized lands. Urbanized settings contain impervious surfaces that are highly prone to pollutant run off such as road salt. Road salt runoff can affect the quality of surface and groundwater resources in addition to having severe impacts on ecosystems and all ecosystem components. Subsequently, surface waters and groundwater within Illinois have shown elevated concentrations of chloride. In a typical winter season in Illinois, about 471,000 tons of road salt are deposited. About 45% of the deposited road salt will infiltrate through the soils and into shallow aquifers. A small percentage of chloride remains in the subsurface feeding shallow aquifers during the non-salting season. Chloride has the potential to reside within groundwater for years based on the pathway, the geologic material, and the recharge rate of the aquifer system. However, the relationship between road salt application rates, residence times, and net mass accumulation of chloride have not been studied. The transport and fate of chloride in Little Kickapoo Creek watershed (LKCW) was modeled utilizing MODFLOW, MODPATH, and MT3D. An increase in application rate showed increases in the mass of chloride within LKCW. Chloride concentrations reached maximum contaminant level of 250 mg/L after 10 years of deposition exhibiting how quickly the solute builds up within LKCW. Allowing the solute to return to safe drinking levels within the watershed took 30 years. Steady-state times varied based on application rates, lower rates of 1,000 mg/L to 2,500 mg/L took about 60 years, higher rates never achieved steady-state conditions. Model simulations reveal a positive relationship between application rate and residence time, the average time a molecule resides within the reservoir, of chloride. At steady-state conditions, the Cl- residence time reflects that of groundwater (~1,000 days). Prior to steady-state conditions, residence time varies from 1,123 to 1,288 days based on application rate.

Comments

Imported from ProQuest Ludwikowski_ilstu_0092N_10729.pdf

Page Count

67

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